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| United States Patent |
5,725,770
|
|
Henry
|
March 10, 1998
|
Waste treatment plant and process
Abstract
A waste treatment process including the steps of: (i) passing waste
material which may comprise animal or human faeces comprising an insoluble
component such as lignocellulose through a bioreactor system including a
plurality of bioreactors in series and maintaining said insoluble
component as a suspension in said waste material; and (ii) separating
suitably by filtration the insoluble component from the waste material. A
waste treatment plant including: (i) a bioreactor system including a
plurality of bioreactors in series for treatment of waste material; (ii)
means such as filtration for separating an insoluble component from said
waste material after passage through the bioreactor system.
| Inventors:
|
Henry; Dick P. (Brisbane, AU)
|
| Assignee:
|
Fungi-Gulp Pty. Ltd. (Queensland, AU)
|
| Appl. No.:
|
704595 |
| Filed:
|
September 16, 1996 |
| PCT Filed:
|
March 16, 1995
|
| PCT NO:
|
PCT/AU95/00145
|
| 371 Date:
|
September 16, 1996
|
| 102(e) Date:
|
September 16, 1996
|
| PCT PUB.NO.:
|
WO95/25071 |
| PCT PUB. Date:
|
September 21, 1995 |
Foreign Application Priority Data
| Current U.S. Class: |
210/603; 210/180; 210/201; 210/255; 210/612; 210/631; 210/764 |
| Intern'l Class: |
C02F 003/12; C02F 011/14 |
| Field of Search: |
210/603,605,612,613,620,621,631,764,175,177,903,179-183,195.1,199,201,255
|
References Cited
U.S. Patent Documents
| 4246099 | Jan., 1981 | Gould et al. | 210/603.
|
| 5228995 | Jul., 1993 | Stover | 210/180.
|
| 5290450 | Mar., 1994 | Kobayashi | 210/613.
|
| 5380438 | Jan., 1995 | Nungesser | 210/605.
|
| 5470481 | Nov., 1995 | Modell et al. | 210/175.
|
| 5514277 | May., 1996 | Khudenko | 210/631.
|
| 5616241 | Apr., 1997 | Khudenko | 210/195.
|
| Foreign Patent Documents |
| 13128/76 | Apr., 1976 | AU.
| |
| 58023/80 | Nov., 1980 | AU.
| |
| 85687/82 | Jan., 1983 | AU.
| |
| 36004/84 | Jun., 1985 | AU.
| |
| 56223/86 | Sep., 1986 | AU.
| |
| 15279/88 | Nov., 1988 | AU.
| |
| 16269/88 | Nov., 1988 | AU.
| |
| 53620/90 | Aug., 1990 | AU.
| |
| 52773/90 | Sep., 1990 | AU.
| |
| 61544/94 | Sep., 1994 | AU.
| |
| 087127 | Aug., 1983 | EP.
| |
| 60/084198 | May., 1985 | JP.
| |
| 1151515 | Apr., 1985 | SU.
| |
| 1171-436 | Aug., 1985 | SU.
| |
| 1404468 | Jun., 1988 | SU.
| |
Other References
Blachford, et al., "Oxygenated Activated-Sludge Process: Evaluation at
Palmersford", Journal of the Institute of Water Pollution Control, vol.
81, No. 5, pp. 601-618, 1982.
|
Primary Examiner: Wyse; Thomas G.
Attorney, Agent or Firm: Madson & Metcalf
Claims
I claim:
1. A waste treatment process including the steps of:
(i) passing waste material comprising an insoluble component through a
bioreactor system including a plurality of bioreactors in series and
maintaining said insoluble component as a suspension in said waste
material;
(ii) passing treated waste material from said bioreactor system to one or
more acidification tanks to reduce the pH below 4.5 to produce free
volatile fatty acids for elimination of bacterial pathogens in said
treated waste material; and
(iii) separating the insoluble component from the waste material before or
after step (ii).
2. A process as claimed in claim 1 including a further step of treating
waste material to remove nitrogen in the form of ammonia, dissolved
phosphorous and carbon as volatile fatty acids.
3. A waste treatment process as claimed in claim 1 wherein said waste
material is agitated each bioreactor so that said waste material is
maintained in the form of a slurry or suspension to maintain said
insoluble component in a suspended state.
4. A waste treatment process as claimed in claim 1 wherein said waste
material in each bioreactor is heated to a temperature of between
25.degree.14 50.degree. C.
5. A waste treatment process as claimed in claim 4 wherein the temperature
is maintained between 30.degree.-40.degree. C.
6. A waste treatment process as claimed in claim 5 wherein the waste
material is initially at a temperature of 40.degree. C. in said bioreactor
system before the temperature is slowly decreased to 30.degree. C.
7. A waste treatment process as claimed in claim 1 wherein the pH in said
bioreactor system is maintained between 5.0-7.0.
8. A waste treatment process as claimed in claim 7 wherein the pH is
maintained between 5.8-6.4.
9. A waste treatment process as claimed in claim 1 wherein said waste
material is maintained in each bioreactor for 12-48 hours.
10. A waste treatment process as claimed in claim 9 wherein said waste
material is maintained in each bioreactor for 24 hours.
11. A waste treatment process as claimed in claim 1 wherein the waste
material after leaving the bioreactor system is passed through a filter or
sieve to filter out the insoluble component.
12. A waste treatment process as claimed in claim 11 wherein a liquid
fraction remaining after removal of the insoluble component is passed into
said one or more acidification tanks for a period of 24-48 hours.
13. A waste treatment process as claimed in claim 2 wherein said waste
material after passage through said one or more acidification tanks is
passed through a hanging curtain assembly for removal of said nitrogen in
the form of ammonia, dissolved phosphorous and carbon as volatile fatty
acids.
14. A waste treatment process as claimed in claim 1 wherein the pH is
reduced to a value of between 4.0-4.5.
15. A waste treatment process as claimed in claim 1 wherein an atmosphere
of carbon dioxide or effluent gases is maintained in the or each
acidification tank to inhibit growth of bacterial pathogens.
16. A waste treatment plant including:
(i) a bioreactor system including a plurality of bioreactors in series for
treatment of waste material;
(ii) one or more acidification tanks to reduce the pH below 4.5 to produce
free volatile fatty acids for elimination of bacterial pathogens in said
treated waste material; and
(iii) means for separating an insoluble component from said waste material
after passage through the bioreactor system.
17. A waste treatment plant as claimed in claim 16 wherein each bioreactor
is connected to an adjacent bioreactor by transfer conduit.
18. A waste treatment plant as claimed in claim 16 wherein each of said
bioreactors are supported on a slope with an initial bioreactor located on
a more elevated position than a final bioreactor.
19. A waste treatment plant as claimed in claim 16 wherein there is
provided heating means in each bioreactor to maintain an operational
temperature of between 30.degree.-40.degree..
20. A waste treatment plant as claimed in claim 19 wherein said heating
means includes means for injection of steam into each bioreactor.
21. A waste treatment plant as claimed in claim 20 wherein there is
provided a steam boiler connected to a steam conduit which is connected to
injection conduits which communicate with each bioreactor.
22. A waste treatment plant as claimed in claim 19 wherein there is
provided thermostatically controlled means to maintain said operational
temperature in each bioreactor.
23. A waste treatment plant as claimed in claim 16 wherein each bioreactor
is provided with agitation means to maintain said waste treatment material
in a suspended state.
24. A waste treatment plant as claimed in claim 16 wherein said separating
means includes a filter or sieve to separate said insoluble component from
a liquid fraction of said waste material.
25. A waste treatment plant as claimed in claim 16 wherein there is
provided means to maintain an atmosphere of carbon dioxide or other gas in
said acidification tank(s) to inhibit growth of yeasts.
26. A waste treatment plant as claimed in claim 25 wherein said means to
maintain an atmosphere of carbon dioxide includes transfer means to
transfer effluent gases generated in said bioreactor system to said
acidification tank(s).
27. A waste treatment plant as claimed in claim 26 wherein said gases from
said acidification tank(s) are transferred to gas scrubbers for discharge.
28. A waste treatment plant as claimed in claim 16 wherein there is further
provided a treatment means in communication with said one or more
acidification tanks to remove nitrogen in the form of ammonia, dissolved
phosphorous and carbon as volatile fatty acids from said waste material.
29. A waste treatment plant as claimed in claim 28 wherein said treatment
means includes a hanging curtain assembly.
Description
FIELD OF THE INVENTION
THIS INVENTION relates to a waste treatment plant and process.
BACKGROUND ART
Hitherto disposal of waste including faeces from livestock feedlots
including piggeries, beef cattle feedlots, dairy cattle milking sheds and
holding yards, and poultry farms which were operated on a large scale
commercial basis has been a time consuming and expensive process. This was
mainly because of the problem of effective disposal of an insoluble or
undigested solid or sludge component which was mainly formed from animal
faeces which was sometimes mixed with undigested livestock feed. Animal
faeces contains proteins, protein breakdown products, fats, complex
carbohydrates and lignocellulose. Lignocellulose is an amorphous matrix of
hemicellulose and lignin. Hemicelluloses are polysaccharides which are
usually branched and formed from sugars and uronic acids. Lignins are
highly cross-linked aromatic polymers of no regular repeating unit because
of their formation by free radical condensation. Lignocellulose in the
animal faeces is derived from barley (e.g. barley awns), lucerne, sorghum
and other stockfeeds.
Reference is made to Australian Patent Application 91080/91 (ie.
International Patent Application PCT/AU91/00587 which was published under
WO 92/11210) which describes a waste treatment process and plant which
comprises passing biological waste through one or more hanging curtains
made from two layers of a soft reticulated polyurethane foam and a
reinforcing layer of synthetic material interposed therebetween. The
curtains formed a support for filamentous micro-organisms which formed a
dense mat of cellular material. The micro organisms remove dissolved
phosphorus, nitrogen in the form of ammonia and carbon as organic acids
from the biological waste.
The process of Specification WO 92/11210 was extremely efficient in
processing biological waste from distilleries and breweries as well as
glycerol waste because this waste did not require an initial anaerobic
fermentation step which is necessary in relation to waste from livestock
feedlots as described above. As stated in Specification WO 92/11210
non-fermented biological waste must be subjected to an anaerobic
fermentation step so as to break down complex macromolecules such as
carbohydrates, proteins, lipids to organic acids of 8 carbon atoms or
less. This fermentation step takes place usually in the presence of
acidogenic fermentative bacteria which may produce organic acids such as
volatile fatty acids which may be readily metabolised to carbon dioxide by
the hanging curtain technology described above.
After the fermentation period was completed which usually took 5 days or
more soluble digestible matter was collected as supernatant and separated
from the insoluble or undigested sludge component discussed above which
contained lignocellulose.
The conventional methods for disposal of the indigestible material included
passing the indigestible material to anaerobic ponds, septic tanks or
pits. Alternatively the indigestible material was dewatered by filtration
or by drying on open or covered sand beds. The dried sludge was
subsequently incinerated or used as fertiliser. In some cases the
indigestible material was used as landfill.
However it will be appreciated from the foregoing that the presence of the
indigestible material in the anaerobic fermentation tank or digester meant
that fermentation had to be stopped at periodic intervals of time to
remove the indigestible material which was time consuming, wasteful and
expensive.
The indigestible material also could not be spread onto anaerobic ponds or
used as landfill in Moslem countries such as Malaysia or Indonesia. In
countries where this method of disposal could be achieved, it was
relatively expensive because of the transportation costs.
The presence of the indigestible material in the anaerobic digester also
was undesirable in that it accumulated in the digester over a period of
time and inhibited the fermentation reaction proceeding in an efficient
manner because of the production of phenolic compounds. These compounds
were also toxic to the filamentous micro-organisms used in the hanging
curtain technology of Specification WO/9211210.
It will also be appreciated that the indigestible material also contained
many pathogenic microorganisms after the anaerobic fermentation step which
were not eradicated prior to the pumping of the indigestible material as a
slurry into anaerobic ponds or when spread onto land and thus caused
disease or infection. To avoid this possibility it was necessary, as
discussed in Henry et al Journal Appl Bact. 55 89-95 (1983), to reduce the
pH of the indigestible material to pH 4.5 or lower (ie. below the pKa of
the volatile fatty acids). In this regard it will be appreciated that free
volatile fatty acids can eliminate bacterial pathogens.
SUMMARY OF THE INVENTION
It therefore is an object of the invention to provide a process and plant
for waste treatment which may alleviate at least to a certain extent the
problems described above in regard to efficient disposal of the insoluble
or undigested sludge component containing lignocellulose.
The process of the invention includes the following steps:
(i) passing waste material comprising an insoluble component through a
bioreactor system including a plurality of bioreactors in series and
maintaining said insoluble component as a suspension in said waste
material;
(ii) passing treated waste material from said bioreactor system to one or
more acidification tanks to reduce the pH below 4.5 to produce free
volatile fatty acids for elimination of bacterial pathogens in said
treated waste material; and
(iii) separating the insoluble component from the waste material before or
after step (ii).
There is also provided a waste treatment plant including:
(i) a bioreactor system including a plurality of bioreactors in series for
treatment of waste material;
(ii) one or more acidification tanks to reduce the pH below 4.5 to produce
free volatile fatty acids for elimination of bacterial pathogens in said
treated waste material; and
(iii) means for separating an insoluble component from said waste material
after passage through the bioreactor system.
The waste material which is subject to the process of the invention
suitably includes human or animal faeces and preferably faeces from
livestock feedlots as described above which may have a stockfeed component
containing lignocellulose.
Each bioreactor may be interconnected by an overflow conduit so that waste
material or influent i s quickly and efficiently transferred from one
bioreactor to an adjacent bioreactor without the need for pumping material
so as to transfer material from one bioreactor to another.
Each bioreactor is suitably provided with agitation means which keeps the
contents of each bioreactor in the form of a slurry or suspension so that
the solid particles are maintained in the suspended state to achieve the
object of the invention.
The contents of each bioreactor are also suitably subject to appropriate
heating means and in one form this may be provided by steam being passed
into and out of each bioreactor. However, other forms of heating means may
be utilised such as electrical heating. Preferably the temperature in each
bioreactor is maintained at a desired temperature by suitably
thermostatically controlled means between 25.degree.-50.degree. C. and
more suitably 30.degree.-40.degree. C. In a preferred form the temperature
is slowly decreased as the waste material passes through each bioreactor
from initially 40.degree. C. to finally 30.degree. C.
Preferably the pH of the waste material fed into the bioreactors is
maintained between 5.0-7.0 and more suitably between 5.8-6.4. The
retention time in each bioreactor may be 12-48 but more suitably 24 hours.
After the waste effluent leaves the bioreactor system it may be passed
through a filter or sieve to filter out the insoluble material which is
preferably incinerated or if it is to be spread onto land it may be passed
through acidification tanks as described hereinafter. It will be
appreciated that removal of the insoluble material may take place in any
suitable manner. While filtration is a preferred procedure, flocculation
may also be utilised.
The supernatant or soluble liquid from the filter may then be passed into
the one or more acidification tanks and preferably maintained in said
tank(s) for a period of 24-48 hours to reduce the pH to a value of below
4.5 and more suitably between 4.0-4.5 which is below the pKa of the
volatile fatty acids e.g. acetic acid, propionic acid, butyric acid,
valetic acid, caproic acid, enanthic acid as well as octanoic acid as well
as relevant isomers. Such volatile fatty acids (VFAs) are produced by the
anaerobic bioreactor system and the lowering of the pH is to convert VFA
salts to free acid in the acidification tank(s). This will eliminate most,
if not all bacterial pathogens.
In a variation of the above described procedure, in some cases the waste
effluent after it leaves the bioreactor system may be passed through the
acidification tank(s) before removal of the insoluble material. In this
embodiment after removal of the insoluble material the waste effluent may
then be passed to a curtain assembly as described hereinafter. This
procedure is preferable when it is impossible to incinerate the insoluble
material after filtration of the waste material after passage of the waste
material through the bioreactor system.
There also may be provided means for maintaining an atmosphere of carbon
dioxide or other gas in said acidification tank(s) to inhibit the growth
of yeasts in said acidification tank(s). Such means may, for example,
comprise conduit(s) for the carbon dioxide or other gas which extend into
the or each acidification tank. Such conduits may be connected to a
suitable source of carbon dioxide or said other gas.
Preferably in this embodiment there is provided means such as appropriate
transfer conduits for transferring effluent gases (which may include
carbon dioxide) generated in the bioreactor system to the acidification
tank(s) to maintain a gaseous atmosphere above the waste material being
acidified. This feature as stated above is useful in that it inhibits the
growth of yeasts or fungi in the acidification tank(s) such as Candida
ingens. The gases may subsequently be removed from the acidification
tank(s) by appropriate conduit(s) to gas scrubbers for eventual discharge.
Preferably the waste material is subjected to a further treatment step to
remove nitrogen in the form of ammonia, dissolved phosphorous and carbon
in volatile fatty acids. More preferably a suitable means for removing
nitrogen in the form of ammonia, dissolved phosphorous and carbon is a
hanging curtain assembly. In this particular embodiment, the waste from
the acidification tank(s) may be passed to a hanging curtain assembly,
which maybe, for example, a hanging curtain assembly of the of the type
described in Patent Specification 91080/91. Some of the carbon is evolved
as carbon dioxide with the remainder being retained by the micro-organisms
contained therein in the hanging curtain assembly.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference may now be made to a preferred embodiment of the invention as
shown in the attached drawings wherein:
FIG. 1 is a flow diagram of a waste treatment plant constructed in
accordance with the invention;
FIG. 2 is a flow diagram of an alternative form of waste treatment plant
constructed in accordance with the invention.
DETAILED DESCRIPTION
In FIG. 1 there is shown an in-ground holding tank 10 for influent
comprising faeces admixed with undigested feed or waste feed from a
piggery (not shown). The influent is pumped by a feed pump 11 through a
macerator 12 which grinds the particles in the influent into small pieces
or finely divided material before the influent is passed into bioreactor
13 provided with agitator 14 having shaft 15 mounted in bearing 16. There
is also provided conduit between holding tank 10 and macerator 12, conduit
18 between feed pump 11 and macerator 12 and conduit 19 which provides
communication between inlet conduit 20 and bioreactor 13. Conduit 20 is
provided with a shut off valve V.sub.1 and flow control diaphragm valve
V.sub.2. Conduit 21 functions as a return line for recycling influent from
bioreactor 13 through conduit 20 back to holding tank 10 which depends
upon operation of valves V.sub.1 and V.sub.2.
There is also provided additional bioreactors 13A, 23B, 13C, 13D and 13E
all having a similar construction to bioreactor 13. There is provided
overflow conduits 22 between adjacent bioreactors for transfer of fluid.
Each bioreactor is also provided with a drain line 23 having a shut off
valve V.sub.1.
There is also provided a steam boiler 24 into which raw water is fed
through conduit 25 also provided with a single valve V.sub.1. Steam may
then pass into conduit 26 having a pressure control valve assembly 27.
There is also provided a plurality of steam conduits 28 which each
communicate with supply conduit 26 as shown which pass steam into each of
the bioreactors 13-13E as shown. Each steam conduit 28 is also provided
with a vacuum breaker valve V.sub.3 to stop back siphonage of fluid as
shown. There is also provided a shut off valve V.sub.1 in each conduit 28
as well as a further valve V.sub.1 associated with a temperature control
valve 29 in the form of a sliding gate valve associated with conduit 30
which also has a thermostat or thermostat controller 31 in the form of a
probe which extends into each bioreactor which controls the temperature
attained in each bioreactor 13-13E.
There is also provided an outlet conduit 32 with each bioreactor 13-13E
which each communicates with conduit 33 for passing effluent gases to
tanks 48, 50 and 56 described hereinafter via transfer conduit 32A and
inlet conduits 33A, 33B, and 33C. Effluent gases may then pass through a
return line 34A from gas line 49A to a pair of gas scrubbers 34 connected
in parallel as shown. The bottom gas scrubber 34 has an associated conduit
35 and the top gas scrubber 34 has an associated conduit 36. Each of
conduits 35 and 36 are shut off with valves V.sub.4 and communicate with
conduit 37 which communicates with fan 38 and stack 39. There is also
provided steam trap 40. Valves V.sub.4 function to take one of scrubbers
34 out of service for maintenance purposes.
The effluent after it passes out through the final bioreactor 13E is passed
through a feed pump 41 through conduit 42 and subsequently through conduit
43 to a sludge filter 44. Pressure indicators 51 are shown associated with
conduit 43 as well as conduit 47. A solid fraction 45 from sludge filter
44 is retained in container 46 whereby solid fraction 45 which is mainly
lignocellulose may be transferred by truck 46A for incineration or other
form of disposal. A liquid fraction rich in volatile fatty acids or VFAs
is then passed to a VFA feed tank 48 through conduit 47 where it is held
for 2 days before being passed through conduit 52 to a transfer pump 53
before being fed into VFA holding tank 50 via conduit 54 which
communicates with conduit 55.
Conduit 28A functions to transfer steam from conduit 26 to a VFA liquid
acidification tank 56 which is fed with sulfuric acid (H.sub.2 SO.sub.4)
from a sulfuric acid feed tank 57 which is associated with an inlet
conduit 58 having a pressure relief valve V.sub.5 and a drain conduit 59
which communicates with conduit 62 which passes through a sulfuric acid
pump 60. There is also provided a sump 61. The sulfuric acid is passed
through conduit 62 which communicates with conduits 58 and 59 as shown to
acidification tank 56 which is also provided with an agitator 14 as shown.
Each of agitators 14 and associated shafts 15 in bioreactors 13--13E as
well as tank 56 are provided with a variable speed control (VS) shown in
phantom. Material may be passed from tank 56 to conduit 52 through conduit
49 which thereafter may be transferred to conduit 55 and hence to tank 50
or alternatively to tank 56 though conduit 57 depending upon operation of
shut off valves V.sub.1.
There is also provided conduits 64, 63 and 65 which each communicate with
tanks 48, 56 and 50 respectively for transferring effluent gases back into
gas line 49A and subsequent flow through return line 34A. Conduit 67 is
also shown having temperature controller 31 for control of temperature in
tank 56. Conduit 67 communicates with conduit 28A as shown via temperature
control valve 29.
Tank 50 is also provided with temperature indicator 68 and tank 56 is also
provided with pH indicator 69 as shown.
Liquid from VFA holding tank 50 is passed to a hanging curtain assembly 70
through conduit 71 and passed through a curtain feed pump 72 provided with
a variable speed control VS. Conduit 71 may be split into separate
conduits 73 and 74, 75 and 76 as well as 77 and 78 which may apply liquid
waste as shown to either side of a curtain module or curtain subassembly
79A. There also may be utilised three additional sub-assemblies 79B if
required to increase the waste treatment capacity of hanging curtain
assembly 70. The flow connections of sub-assemblies 79B to pump 72 are
omitted for clarity. Each of sub-assemblies 79A and 79B are retained in a
housing 80 having a sloping drain floor 81. There is also utilised a
temperature indicator 82 which is associated with housing 80.
Gases from housing 80 may be passed through conduit 83 through damper valve
V.sub.6, cooling fan 84, and stack 85. There is also shown a further
damper V.sub.6 which communicates with the interior of housing 80 and the
operation of each damper valve V.sub.0 controls air flow through housing
80. Preferably the air pressure inside housing 80 is maintained less than
atmospheric.
Waste effluent may be passed from the sloping floor 81 of housing 80 to a
treated waste holding tank 86 having a discharge pump 87 associated
therewith via conduit 86A. There is also provided a level element 91 which
may control pump 87 for maintaining the level of fluid in housing 80.
There is also provided pH indicator 89. Fluid may be pumped by pump 87
through discharge conduit 88 which has a return line 89A. Waste may be
recycled through conduit 90 to housing 80 as shown from conduit 88.
Thereafter waste may be passed to a treatment pond 92 which communicates
with another pond 93 via conduit 94 with the assistance of pump 95. Waste
may subsequently be transferred to a feed tank 96 via conduit 97.
Thereafter conduit 97A may pass fluid to a treatment channel or flume 98
of a piggery. Subsequently fluid may be passed to holding tank 10 via a
bypass plate 99 or alternatively through a conduit 100 to an in ground
holding tank 101 having a discharge pump 102 which may transfer fluid to
treatment pond 92 through conduit 103.
In an alternative arrangement as shown in phantom material from conduit 88
may be transferred through conduit 104 to a filter 105 whereby a solid
fraction 107 may be deposited in container 106 before being removed by
truck 108A for incineration or other form of disposal. A liquid fraction
may be passed from filter 105 via conduit 105A to a liquid tank whereby it
may be recycled to flume 98 via conduit 109 and with the assistance of
pump 110.
FIG. 2 represents a modified waste treatment plant in contrast to the waste
treatment plant shown in FIG. 1. Similar reference numerals are utilised
for the sake of convenience. One difference between the FIG plant and the
FIG. 2 plant is the adoption of bioreactors 13-13F on a slope as indicated
with overflow conduits 22 facilitating transfer of fluid from adjacent
bioreactors. Valves are also not indicated for the sake of convenience.
One conduit 18 interconnects holding tank 10 and bioreactor 13 and steam
from boiler 24 flows through conduit 26 and subsequently through inlet
conduits 28 to a respective bioreactor 13-13F. Exhaust conduits 32 for gas
also communicate with main transfer conduit 33 as described above in the
FIG. 1 waste treatment plant.
Gas is passed to acidification tanks 56A and 56B through conduit 33 and
into each tank through inlet conduits 33A and 33B as shown. There is also
supplied a gas return line 34A to gas scrubbers 34.
In a variation of the procedure shown in FIG. 1, the waste effluent or
waste material after emerging from the final bioreactor 13F may be
transferred directly to acidification tank 56A through conduit 44A shown
in phantom. In this variation the waste material will still have the
insoluble component entrained therein so that the waste material may then
be transferred from acidification tank 56B to filter 44 after passage
through conduit 45A also shown in phantom. Subsequently, after filtration
the liquid fraction may then be transferred to curtain assembly 70 through
conduit 46A also shown in phantom.
Another difference is the adoption of two VFA liquor acidification tanks
56A and 56B whereby a liquid fraction from sludge filter 44 is passed
through conduit 47 and subsequently into tank 56A. Sulphuric acid is
pumped by pump 60 from a tank or drum 57 via conduit 62 to tank 56A.
Material may then be passed from tank 56A to tank 56B through conduit 62A.
Acid treated fluid may then be passed to curtain assembly 70 through
conduit 71.
Waste liquid after passing through curtain assembly 70 is passed to filter
feed tank 86 through conduit 86A whereafter fluid is pumped by pump 87 to
treatment pond 92 by conduit 88 or passed through recycling conduit 90 to
curtain assembly 70 after passage through conduit 104A. Liquid from pond
92 is passed through conduit 97 back to flume 98 with the agency of pump
95. Fluid may also be passed to filter 105 from curtain assembly 70
through conduit 104A whereby a liquid fraction may be passed to treatment
tank 108 through conduit 105A whereafter fluid may be passed to conduit 97
through conduit 109 assisted by pump 110.
The waste being passed through the series of bioreactors is serially
digested by a different population of flora in each tank. The short mean
residue time in each tank (.about.24 hours) permits a specific flora to
develop in each tank and progressively digest the material being passaged.
The end result is the product of volatile fatty acids (VFAs) i.e. C.sub.2
-C.sub.8 (acetic, propionic, butyric, valeric, caproic, heptanoic and
octanoic acids and relevant isomers). Non-volatiles such as lactic and/or
succinic acids are not produced. Traces (.about.-3 mML.sup.-1) of
phenylacetic acid do appear. The purpose of restricting the end products
of fermentation to VFAs ensures an excess of these acids is present to
effect destruction of bacterial pathogens present in the waste.
The serial fermentation also enables conditions of pH, fermentation and
residue time in each bioreactor to be manipulated in order to optimise
production of the VFAs.
______________________________________
WASTE TREATMENT PLANT
DESIGN CRITERIA
______________________________________
1.0 GENERAL
Atmospheric Pressure 101.325 kPa
Min Design Temperature 15.degree. C., 50% relative
humidity
Max Design Temperature 32.degree. C., 100% relative
humidity
Operating Schedule 7 days/week, 24
hours/day
2. FEED DEFINITION
Feed Material Piggery flume floor
flushings
Treatment Capacity 1500 L/day
Feed % Solids 3% w/v
Solids Size Range 2-5 mm
Feed pH 5.8-6.4
Design Temperature - Min
20.degree. C.
Design Temperature - Max
30.degree. C.
Design Availability 85%
Design Flow 73.5 L/h
3.0 FEED TANK
Type Inground
Material Concrete
Retention Time 24 hours
Capacity 1500 L nominal
Temperature 20.degree. C.-30.degree. C.
4.0 ANAEROBIC BIOREACTORS
No. Stages 6
Retention Time per stage
24 hours
Temperature Reaction 1 40.degree. C.
2 35.degree. C.
3 35.degree. C.
4 35.degree. C.
5 30.degree. C.
6 30.degree. C.
% of solids fermented 45%
Tank material FRP (Isophthalic)
Agitation Suspension (0.25
kW/m.sup.3 approx)
S.S. 316 A310
impeller
5.0 FERMENTATION PRODUCT
pH 5.8-6.4
Temperature 30.degree. C.
% Solids 1.5% w/v
Solids Composition Lignocellulose
6.0 POST FERMENTATION FILTRATION
Filtration Rate L/m.sup.2 .multidot. h
Filter Cake Moisture % moisture wet
basis
Product Calorific Value
20 MJ/kg, air-dry
Kg Product per Day 25
7.0 ACIDIFICATION
Retention Time (batch) 48 hours
No. Tanks 3 (series batch)
pH after Acidification 4.5
Acid Addition Rate 2-3 mL H.sub.2 SO.sub.4 per L
filtrate
Temperature Natural
Acid Consumption 3-4.5 L/day
Acid Storage 200 L drums
Acid Delivery Via drum pump or
manual
container
addition
8.0 FEED TO CURTAINS
Analysis
Acetic Acid 137 mmol/L 0.82% w/V
Propionic Acid
37 mmol/L 0.27% w/v
Butyric Acid
38 mmol/L 0.33% W/V
Valeric Acid
10 mmol/L 0.10% w/v
Caproic Acid
3.1 mmol/L 0.04% w/v
Total Volatile Fatty Acids
1.57% w/v
Feed rate - average 62.5 L/h
design
73.5 L/h
pH 4.5
Temperature 30.degree. C.
9.0 CURTAIN MODULE
Curtain Treatment Capacity
40-100 L/m.sup.2 day
No. Curtains 3
Curtain Fall 3 m or greater
Operating Temperature - Max
37.degree. C.
Air Temp in 28.degree. C.-32.degree.
% Relative Humidity 90%
% Relative Humidity 100%
Distance between curtains
150 mm
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